1. Technical Field
The present invention relates to a method of patterning a multiple-layered resist film and a method of manufacturing a semiconductor device.
2. Related Art
In processes for manufacturing semiconductor devices, a material patterning is generally carried out by a lithography process to form patterned photoresist film and a successive dry etching process using the patterned photoresist film as a etching mask.
As scaling down of semiconductor device proceeds, there needs to form device elements with a narrower pitch and a higher aspect ratio photoresist pattern, resulting in a reduced margin in lithgraphy process and a reduced mechanical stability of the patterned photoresist film against applied stress. One solution is to reduce the photoresist film thickness, but attended with insufficient etch resistivity of the photoreasist mask. A proposed solution for the issue is a method of patterning through a multiple-layered resist film, including: first of all, transferring a pattern onto an upper resist film; etching an underlying thick resist film through a mask of the upper patterned resist film; and etching a target material to be etched through a mask of the thick resist film.
Typical two types of patterning processes employing a multiple-layered resist film, a process employing a dual-layered resist film, and a process employing ternary-layered resist film, will be described.
The patterning process employing a dual-layered resist film involves, as shown in FIG. 12A, sequentially depositing a lower layer resist film 14 and a silicon-containing upper layer resist film are on a target film 12 to be etched, and the silicon-containing upper layer resist film is exposed to light to transform a pattern of a photomask (not shown) onto a silicon-containing upper layer resist film 16. Then, as shown in FIG. 12B, a pattern on the upper layer resist film 16 is transferred onto the lower layer resist film 14 by a reactive ion etching (RIE) process. Typical etching gas employed is an oxygen(O2)-based gaseous mixture, in order to maintain sufficient etch selectivity for the silicon-containing upper layer resist film 16 against the organic film serving as the lower layer resist film 14.
Then, the pattern of the lower layer resist film 18 (and the silicon-containing upper layer resist film 16) is transferred onto the underlying target film 12 by dry etching process.
In a patterning process employing a ternary-layered resist film, as shown in FIG. 13A, a lower layer resist film 14, a silicon-containing interlayer 15 (for example, spin on glass-applied film (SOG film)) and an upper layer resist film are sequentially deposited on a target film 12, and then, the upper layer resist film is exposed to light to transform a pattern of a photomask (not shown) onto an upper layer resist film 17.
Next, as shown in FIG. 13B, the pattern on the upper layer resist film 17 is transferred onto the silicon-containing interlayer 15 by a RIE using a fluorocarbon-containing gas to form a patterned silicon-containing intermediate layer 20. Next, the pattern of silicon-containing intermediate layer 20 is transferred onto the lower layer resist film 14 by dry etching. Typical etching gas employed is an oxygen (O2)-based gaseous mixture. Thereafter, similarly as in the case of the dual-layered resist, the pattern of the lower layer resist film 22 is transferred onto the underlying target film 12 by dry etching process.
As described above, thickness of the upper layer resist film can be reduced by utilizing a multiple-layered resist film, and a decrease in aspect ratio of the patterned resist film can be solved by processing the thicker lower layer resist film by a dry etch process with higher selectivity.
A typical etching gas employed for performig dry etching process for removing the lower layer resist film 14 is a gaseous mixture of He gas and O2 gas described in Japanese Patent Laid-Open No. H5-29,211 (1997). In addition, a gaseous mixture of O2 gas and a reduction gas is described in Japanese Patent Laid-Open No. H5-217,883 (1997), and carbon monoxide (CO) gas, disilane gas and the like are exemplified as the reduction gas. In Japanese Patent Laid-Open No. 2002-110,643, a gaseous mixture of O2 gas with nitrogen (N2) gas or CO gas is described.
Further, Japanese Patent Laid-Open No. 2002-14,474 describes an example of etching the lower layer resist film, which utilizes the upper layer resist film composed of a silicon-containing compound and employs an etching gas of a gaseous mixture containing O2 gas and argon (Ar) gas at a vacuum level of 75 mTorr.